The present invention relates to a method for fabricating a semiconductor device, and more particularly, to a method for forming a gate structure of a semiconductor device.
A transistor having a recess gate has been proposed to overcome the limitation that a channel length of the transistor decreases as an integration degree of a semiconductor device increases. The recess gate is a gate provided in a recess formed by etching an active region of a semiconductor device. The recess gate makes it possible to increase a channel length corresponding to a depth of the recess.
Formation of the recess gate, however, requires two masking processes. One is a masking process of forming a recess and the other is a masking process of pattering a gate. Therefore, misalignment may occur between the recess and the gate. Such misalignment between the recess and the gate causes a self-aligned contact (SAC) failure. For example, a bridge phenomenon may occur between a landing plug contact and a gate during a subsequent process of forming the landing plug contact due to the misalignment.
Although a recess gate structure can somewhat overcome the limitation of a decrease in a channel length of a transistor, there are still other limitations caused by a narrow space between gates according to an increase in an integration degree of a semiconductor device.
The narrow space between the gates may cause a contact-not-open phenomenon to take place. In the contact-not-open phenomenon a portion of a substrate to be exposed is not exposed during a subsequent process of forming a landing plug contact. Specifically, a nitride layer, which serves as a barrier during an SAC etching process of forming a landing plug contact, is formed over a gate. As a space between the gates is narrowed, the nitride layer is deposited relatively thickly. Accordingly, the nitride layer deposited on a substrate between the gates is not removed during the SAC etching process, but remains on the substrate, which leads to a contact-not-open phenomenon of a landing plug contact.
To avoid the contact-not-open phenomenon of the landing plug contact, an etching time taken for the SAC etching process to form the landing plug contact may be increased. However, the increase of the SAC etching time may cause a hard mask on a gate to be excessively damaged, resulting in an SAC failure such as a bridge formed between the gate and a subsequently formed contact.
As an alternative to the above method of avoiding the contact-not-open phenomenon of the landing plug contact, the space between the gates may be increased by reducing a linewidth of the gate. However, the reduction in the linewidth of the gate may cause a leaning phenomenon that the gates come into contact with each other because the gates are inclined.
Therefore, with the above-described methods, it is difficult to avoid the contact-not-open phenomenon of the landing plug contact.